Not all environments require a stringent SLA. I have some servers that don't have a stringent SLA and aren't worth being woken up at night over if their disk is filling up fast.
It allows me to remove that big file, then I'm able to run sudo since I don't allow root ssh and sudo won't work with a full disk, then I can clear up space on the system, bring it up again, then update log rotate or do whatever to prevent that case from happening again.
That sounds a lot more complicated (and time consuming) than just having monitoring in place, realizing the disk is filling up and fixing it before it leads to downtime.
Monitoring is in place and usually it is caught in time. Downtime is acceptable in this environment, I don't think its worth being woken up in the middle of the night when it can just be resolved in the morning.
